Multiple Flashes at Constant Pressure and Increasing Temperature

It is possible to stabilize a liquid at a constant pressure by successively flashing it at increasing temperatures as shown in Figure 6-2. At each successive stage the partial pressure of the intermediate components is higher than it could have been at that temperature if some of the lighter components had not been removed by the previous stage. It would be very costly to arrange a process as shown in Figure 6-2, and this is never done. Instead, the same effect is obtained in a tall, vertical pressure vessel with a cold temperature at the top and a hot temperature at the bottom. This is called a “condensate stabilizer.”

Multiple flashes at constant pressure and increasing temperature.

Figure 6-3 shows a condensate stabilizer system. The well stream flows to a high pressure, three-phase separator. Liquids containing a high fraction of light ends are cooled and enter the stabilizer tower at approximately 200 psi. In the tower the liquid falls downward in a process that results in many flashes at ever-increasing temperatures. At the bottom of the tower, some of the liquids are cycled to a reboiler where they receive heat to provide the necessary bottoms temperature (200°F to 400°F). The reboiler could be either a direct-fired bath, an indirect-fired bath, or a heat medium exchanger.

Condensate stabilization system.

The liquids leaving the bottom of the tower have undergone a series of stage flashes at ever-increasing temperatures, driving off the light components, which exit the top of the tower. These liquids must be cooled to a sufficiently low temperature to keep vapors from flashing to atmosphere in the storage tank.

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